The present invention relates to a mixture containing vinylcyclohexane (VCH)-based polymer/copolymer and a stabiliser system, containing lactone, sterically hindered phenol and phosphite component, and to a process for the preparation of said mixture and to the use of the mixture for the manufacture of moulded articles.
In comparison with polycarbonate currently used for the manufacture of optical data stores, homopolymers with sufficient mechanical properties of the vinylcyclohexane-based polymer exhibit a higher viscosity at the same temperature in a wide range of low shear rates.
The lowest possible viscosity is of considerable importance for sufficiently good pit and groove reproduction in injection moulding.
For high densities of data storage of  greater than 5 Gbytes, particularly  greater than 10 Gbytes, accurate reproduction of the smaller and more closely packed pits and the grooves that are possible nowadays is essential. The optical storage media described in EP-A 317 263 and U.S. Pat. No. 4 911 966 are not satisfactory for this use.
In order to obtain the largest possible processing window, high processing temperatures generally above 300xc2x0 C. are required for the homopolymer without a significant decrease in molecular weight occurring.
Generally speaking, a decrease in molecular weight leads to a deterioration in the mechanical properties of polymers. A sufficient level of mechanical properties is, however, necessary for the reliable manufacture of optical discs in injection moulding and for the subsequent manipulation thereof.
In everyday use the material must also be resistant to flexure and fracture.
During machine downtimes in processing it is important to ensure that the material does not suffer a drastic loss of molecular weight during this period.
The phenol and phosphorus stabilisers described in JP 01-294 753, JP 5-242 522 are suitable in high concentrations for limiting the decrease in molecular weight but lead to a considerable decrease in molecular weight at processing temperatures of only about 300xc2x0 C.
JP 61-138648 describes optical data carriers which are manufactured from, i.a. polymethylmethacrylate, polycarbonate and polystyrene, the polymers containing 2-benzofuranones as stabiliser.
The object now is to stabilise VCH-based polymers/copolymers in such a way that processing can take place without a significant decrease in molecular weight, even at high temperatures.
The mixtures according to the invention do not exhibit a significant decrease in the molecular weight of the polymer, even at elevated temperatures.
Surprisingly, it was found that a stabiliser system containing lactone, sterically hindered phenol, and a phosphite component together with vinylcyclohexane-based polymers markedly improves the thermostabilisation for injection-moulded optical data carriers at processing temperatures of  greater than 300xc2x0 C., preferably  greater than 320xc2x0 C., particularly preferably  greater than 330xc2x0 C. and that no significant decrease in molecular weight occurs. Depending on the polymer, degradation processes start to a large extent at temperatures between 350 and 380xc2x0 C. Conventional injection moulding machines permit processing up to about 400xc2x0 C.
The invention relates to a mixture containing A) vinylcyclohexane-based polymer and B) stabiliser system containing lactone, sterically hindered phenol and a phosphite compound.
Component A
The preferred vinylcyclohexane-based polymer comprises a recurring structural unit of the formula (I) 
wherein
R1 and R2, independently of each other, represent hydrogen or C1-C6-alkyl, preferably C1-C4-alkyl, and
R3 and R4, independently of each other, represent hydrogen or for C1-C6-alkyl, preferably C1-C4-alkyl, particularly methyl and/or ethyl, or R3 and R4 jointly represent alkylene, preferably C3 or C4-alkylene, partially condensed 5 or 6-membered cycloaliphatic ring,
R5 represents hydrogen or C1-C6-alkyl, preferably C1-C4-alkyl,
R1, R2 and R3, independently of each another, represent in particular hydrogen or methyl.
The bonding may, apart from the stereoregular head-to-tail bonds, have a small proportion of head-to-head bonds.
The VCH preferably have a predominantly isotactic or syndiotactic diad configuration, more particularly, polymers with a proportion of 50.1 to 74% syndiotactic diads are preferred, more particularly preferably 52 to 70%.
Comonomers which may be used in preference during the polymerisation of the starting polymers (optionally substituted polystyrene) and incorporated in the polymer include: olefins generally having 2 to 10 C atoms such as, for example, ethylene, propylene, isoprene, isobutylene, butadiene, C1-C8 preferably C1-C4-alkyl esters of acrylic and methacrylic acid, unsaturated cycloaliphatic hydrocarbons, e.g., cyclopentadiene, cyclohexene, cyclohexadiene, optionally substituted norbornene, dicyclopentadiene, dihydrocyclopentadiene, optionally substituted tetracyclododecenes, styrenes alkylated on the nucleus, a-methylstyrene, divinylbenzene, vinyl esters, vinyl acids, vinyl ethers, vinyl acetate, vinyl cyanides such as, for example, acrylonitrile, methacrylonitrile, maleic anhydride and mixtures of said monomers. In general, up to 60 wt. % of comonomers based on the polymer may be contained in the polymer, preferably up to 50 wt. %, particularly up to 40 wt. %, most particularly preferably the polymers 1 may contain up to 30 wt. % of comonomers.
The vinylcyclohexane (co)polymers generally have absolute molecular weights Mw (weight-average) of 1000-10000000, preferably 60000-1000000, more particularly preferably 70000-600000, determined by light scattering.
The copolymers may be present both as random copolymers and as block copolymers.
The polymers may have a linear chain structure and have branching sites due to co-units (e.g. graft copolymers). The branching centres include, e.g. star-shaped or branched polymers. The polymers according to the invention may have other geometric shapes of the primary, secondary, tertiary, optionally quaternary polymer structure. Examples include helix, double helix, folded sheet etc. or mixtures of said structures.
Block copolymers include di-blocks, tri-blocks, multi-blocks and star-shaped block copolymers.
Component B
The stabiliser system contains lactone corresponding to formula (I), sterically hindered phenol corresponding to formula (II) and phosphite component corresponding to formula (III), wherein one or more compounds corresponding to formulae (I), (II) and (Il) may be used.
Lactones are preferably compounds corresponding to formula (I) 
wherein
R1, R2, R3 and R4, independently of each other, represent hydrogen or C1-C6-alkyl, preferably C1-C4-alkyl, optionally a 5 or 6-membered ring, preferably cyclohexyl or cyclopentyl. R1 and R2, independently of each other, particularly preferably represent for branched C3-C4-alkyl, particularly iso-propyl and/or tert-butyl.
A particularly preferred lactone is 5,7-di-t-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one. Sterically hindered phenols are preferably compounds corresponding to formula (II) 
wherein
R5 and R6, independently of each other, represent hydrogen or C1-C6alkyl, preferably C1-C4-alkyl, optionally a 5 or 6-membered ring, preferably cyclohexyl or cyclopentyl,
R5and R6, independently of each other, represent particularly preferably C3-C4-alkyl, particularly for iso-propyl and/or tert-butyl,
n represents an integer from 1 to 4, preferably for 3 or 4, particularly 4,
A1and A2, independently of each other, represent C1-C6-alkylene, preferably C1-C4-alkylene, particularly methylene, ethylene,
R, independently, represents hydrogen, C1-C6-alkyl, preferably C1-C4-alkyl, C1-C6-alkoxy, preferably C1-C4-alkoxy, optionally a 5 or 6-membered ring, preferably cyclohexyl or cyclopentyl.
Phosphite components are preferably compounds corresponding to formula (III): 
wherein
R7 and R8, independently of each other, represent hydrogen or C1-C6-alkyl, preferably C1-C4-alkyl, optionally a 5 or 6-membered ring, preferably cyclohexyl or cyclopentyl,
x and y, independently of each other, represent 0, 1, 2, 3, 4, 5, preferably 0, 1 or 2 and
n represents 1 or 2, R7 and R8, independently of each other, stand particularly preferably represent C3-C4alkyl, particularly iso-propyl and/or tert-butyl.
If n =1, the valence bond of the carbon atom in question is attached to hydrogen or C1-C6-alkyl, C1-C6-alkoxy, optionally 5 or 6-membered ring, preferably C1-C4-alkyl, preferably to the radicals named in the case of R7 and R8. 
The structural formulae given reproduce in each case the main components ( greater than 90%) of the industrially used compounds which may contain e.g. isomers, starting compounds and secondary compounds in smaller proportions.
The stabiliser mixture containing a lactone derivative I, sterically hindered phenol II and phosphite component III (phosphonite) is generally used in proportions by weight, based on the polymer used, of 2% to 0.001%, preferably 1% to 0.005%, and more particularly preferably 0.6% to 0.01%.
The proportion of individual components of lactone I, sterically hindered phenol II and phosphite component III (phosphonite) is generally 5 to 95 parts by wt., preferably 10 to 60 parts by wt., the proportions of the individual components adding up to 100.
A mixture more particularly preferred contains the lactone HP 136 (compound I-1) (Ciba Speciality Chemicals, Basel, Switzerland) with a proportion of 5 to 40, particularly 10 to 25 parts by wt., the sterically hindered phenol Irganox 1010 (compound II-1) (Ciba Speciality Chemicals, Basel, Switzerland) with a proportion of 30 to 70 parts by wt., and the phosphonite Irgafos P-EPQ (compound III-1) (Ciba Speciality Chemicals, Basel, Switzerland), with a proportion of 10 to 50 parts by wt., the proportions of the individual components adding up to 100.
The formulae of the compounds I-1, II-1 and III-1 are shown below: 
The lactones, sterically hindered phenols and phosphite compounds are generally well known and available commercially.
The VCH (co)polymers are prepared by polymerising derivatives of styrene with the corresponding monomers by free-radical, anionic or cationic polymerisation or by means of metal complex initiators or catalysts, and the unsaturated aromatic bonds are then hydrogenated wholly or partially (cf. e.g. WO 94/21694, EP-A 322 731).
The vinylcyclohexane-based polymers generally exhibit practically complete hydrogenation of the aromatic units. As a rule, the degree of hydrogenation is xe2x89xa780%, preferably xe2x89xa790%, more particularly preferably xe2x89xa799% to 100%. The degree of hydrogenation can be determined, for example, by NMR or UV spectroscopy.
The starting polymers are generally well known (e.g. WO 94/21694).
The amount of catalyst used depends on the process carried out; this may be carried out continuously, semi-continuously, or batchwise.
The ratio of catalyst to polymer is, for example, generally 0.3-0.001, preferably 0.2-0.005, particularly preferably 0.15-0.01 in the batchwise process.
The polymer concentrations, based on the total weight of solvent and polymer, are generally 80 to 1, preferably 50 to 10, particularly 40 to 15 wt. %.
Hydrogenation of the starting polymers is carried out according to generally well known methods (e.g. WO 94/21 694, WO 96/34 895, EP-A-322 731). A plurality of well known hydrogenation catalysts may be used as catalysts. Preferred metal catalysts are mentioned, for example, in WO 94/21 694 or WO 96/34 896. The catalyst used may be any catalyst known for hydrogenation reactions. Catalysts with a large surface area (e.g. 100-600 m2/g) and a small average pore diameter (e.g. 20-500 xc3x85) are suitable. Also suitable are catalysts with a small surface area (e.g. xe2x89xa710 m2/g) and large average pore diameters which are characterised in that 98% of the pore volume have pores with pore diameters greater than 600 xc3x85(e.g. about 1000-4000 xc3x85) (cf. e.g. U.S. Pat. No. 5.654.253, U.S. Pat. No. 5.612.422, JP-A 03076706). More particularly, Raney nickel, nickel on silica or silica/alumina, nickel on carbon as support and/or noble metal catalysts e.g. Pt, Ru, Rh, Pd are used.
The reaction is generally carried out at temperatures between 0 and 380xc2x0 C., preferably between 20 and 250xc2x0 C., particularly between 60 and 200xc2x0 C.
The conventional solvents which may be used for hydrogenation reactions are described, for example, in DE-AS 1 131 885 (see above).
The reaction is generally carried out at pressures from 1 to 1000 bar, preferably 20 to 300 bar, particularly 40 to 200 bar.
The stabiliser may be introduced at any moment in the preparation process of the vinylcyclohexane-based polymer before or after a process stage in solution, in the solid, liquid or gaseous aggregate stage. The process stages include, optionally, polymerisation which leads to a prepolymer, e.g. polystyrene derivative, optionally hydrogenation of the prepolymer, optionally an evaporation stage, and optionally extrusion or compounding of the vinylcyclohexane-based polymer.
The stabilised vinylcyclohexane-based polymers or copolymers according to the invention are outstandingly suitable for the manufacture of moulded articles and films. These are also particularly suitable for the manufacture of optical data stores, preferably with data storage densities of  greater than 5, particularly  greater than 10 gigabytes, based on a disc with a diameter of 120 mm.
The mixtures according to the invention may contain at least one of the conventional additives such as lubricants and mould release agents, nucleating agents, antistatic agents, stabilisers and dyes and pigments.
The mixtures according to the invention are prepared by mixing the vinylcyclohexane-based polymers or copolymers with the stabiliser system and optionally further additives and compounding at elevated temperatures (generally  greater than 230xc2x0 C.).
Examples of optical data stores include:
magneto-optical disc (MO disc)
mini-disc (MD)
ASMO (MO-7) (xe2x80x9cAdvanced storage magnetoopticxe2x80x9d)
DVR (12 Gbyte disc)
MAMMOS (xe2x80x9cMagnetic Amplifying magneto optical systemxe2x80x9d)
SIL and MSR (xe2x80x9cSolid immersion lensxe2x80x9d and xe2x80x9cmagnetic superresolutionxe2x80x9d)
CD-ROM (Read only memory)
CD, CD-R (recordable), CD-RW (rewritable), CD-I (interactive), Photo-CD
Super Audio CD
DVD, DVD-R (recordable), DVD-RAM (random access memory);
DVD=Digital versatile disc
DVD-RW (rewritable)
PC+RW (Phase change and rewritable)
MMVF (multimedia video file system)
The polymers according to the invention, because of their outstanding optical properties, are also particularly suitable for the manufacture of optical materials, e.g. for lenses, prisms, mirrors, colour filters etc., also as media for holographic images (e.g. cheque cards, credit cards, identification cards, three-dimensional holographic images). The materials may be used as transparent media for inscribing three-dimensional structures e.g. from focused coherent radiation (LASER), particularly as three-dimensional data stores or for three-dimensional reproduction of articles. In view of the low birefringence, the polymers according to the invention are particularly suitable matrix material for photo-addressable polymers. The addition of the stabiliser leads not only to the general effect of themostabilisation but also to better demouldability from the injection mould.